Conventional dispensing guns for dispensing fuels, such as petrol or diesel, may often suffer from spillage of fuel due to fuel dripping from the delivery tube after the delivery of fuel has been stopped, for example by an automatic shut-off arrangement. Even though this is not desirable and may present a small risk of flammable liquid being subjected to an unprotected environment it is generally acceptable with a small leakage of such fuels.
However, in light of the development of new alternative fuels, even such a small leakage may have a detrimental effect and must be avoided. Therefore, various solutions of dispensing guns comprising for example complex outlet valve arrangements and/or means for securing a liquid tight coupling between the dispensing gun and the recipient of the fuel have been developed in recent times. The outlet valve arrangement and/or said securing means of the dispensing guns ensures that no leakage can occur, for example by ensuring that no liquid can be present outside of the outlet valve of the dispensing gun after a dispensing procedure. This can for example be achieved by ensuring that a dispensing procedure is only possible when a coupling part of the dispensing gun has been firmly coupled to a corresponding coupling part associated with the fuel tank of a vehicle, and that the dispensing gun cannot be released before the outlet valve has been completely closed. The outlet valves are often some type of poppet valve. The result of this development is also that any release of a potential overpressure in a dispensing device cannot be made through the dispensing end of the dispensing gun.
Furthermore, there is a demand from a Weights & Measures approvable point of view that none of the measured fuel volume to be dispensed during a dispensing procedure should be able to return to the storage tank of the fuelling facility (or being dispensed through the gun un-measured) thereby ensuring that a customer will receive a correct amount of fuel.
Therefore, a volume of fuel will be trapped between the outlet valve of the dispensing gun and a shut off valve (for example volume measuring device, pump, etc) in the dispenser, or an inlet valve in the dispensing gun, when the dispensing gun has been used for a dispensing procedure.
The trapped liquid may under certain circumstances present a problem. More specifically, the trapped liquid may due to temperature changes expand which in turn may cause a risk of damaging the outlet valve or any other internal component of the dispensing gun. A damage of the outlet valve may in turn influence the operation of the dispensing gun during dispensing of fuel, or ultimately cause a leakage of fuel even when the dispensing gun is not in operation.
The problem of increased pressure resulting from expansion of fuels due to temperature changes is previously known in certain components, other than the dispensing gun, of a fuel dispenser, such as in the hose arranged between the pump and the dispensing gun. It has previously been proposed to solve such problems by arranging some type of pressure relief arrangement, such as an expansion chamber or the like, inside the housing of the fuel dispenser. One such example is disclosed in U.S. Pat. No. 1,963,270 describing a pressure relief attachment arranged between the pump and the hose. Such an expansion chamber is often quite bulky and thus space consuming. Furthermore, while such an expansion chamber works very well in a dispensing system comprising a conventional dispensing gun where a small leakage of fuel is possible, such an expansion chamber may be insufficient in cases where the dispensing gun of a dispensing system is constructed for liquid-tight dispense of fuels. In the latter case, a rise of pressure caused by expansion of liquid may cause damage to components before the increased built-up pressure is equalised in the system and/or a pressure relief arrangement in the fuel dispenser housing is able to compensate for such a rise of pressure.
Furthermore, with the recent developments of dispensing guns, certain dispensing guns may be constructed such that they will comprise a volume of fuel trapped between the outlet and the inlet of the dispensing gun between two dispensing procedures. This may for example be the case where the inlet of the dispensing gun comprises an inlet valve adapted to be closed between to dispensing procedures or if the device measuring the volume dispensed during a dispensing procedure is arranged at or close to the inlet of the dispensing gun instead of at the dispenser end of the hose. It has previously not been considered that expansion of the comparatively small volume trapped inside a dispensing gun may cause any considerable problems. However, with the recent development of dispensing guns ensuring completely liquid-tight guns and couplings thereof, the dispensing guns have become more complex. Arrangement of expansion chambers for example at the end of the hose connected to the metering pump of the dispenser cannot solve the problem of expansion of liquid trapped inside the dispensing gun.
Thus, there is a need to increase the safety of dispensing guns both during a dispensing procedure and between two dispensing procedures.